PARIS • Left-wing outsider Benoit Hamon will fight former prime minister Manuel Valls for the French Socialist presidential nomination on Sunday after winning the first round of the party's primary.

Mr Hamon, 49, was not considered a serious contender when the campaign began last month but the 49-year-old former education minister took the lead with what he called a "message of hope and renewal".

With Europe shifting to the right and the deeply unpopular President Francois Hollande ruling himself out, the Socialist primary has been billed as a fight for the party's soul, with a left-leaning faction represented by Mr Hamon battling Mr Valls' centrist camp.

Mr Hamon scored over 36 per cent, with Mr Valls trailing on 31 per cent, according to results from around 80 per cent of polling stations after Sunday's vote.

Maverick former economy minister Arnaud Montebourg, with 17 per cent, was eliminated and put his support behind Mr Hamon.

The Socialist party, one of the main political forces in France for decades, has become marginalised as Mr Hollande failed to bring high unemployment down and alienated left-wing voters with his economic policies.

Although unlikely to win the presidency this year, the Socialists' final choice on Sunday could still have an impact on the election fortunes of the front runners - Mr Francois Fillon, a conservative; Ms Marine Le Pen, a far-right leader; and Mr Emmanuel Macron, a popular independent.

The photogenic Mr Macron has stolen much of the limelight from his former Socialist government colleagues in recent weeks, with campaign speeches packed.

Polls indicate that Mr Fillon, a former prime minister who has the Republicans ticket, is most likely to win if pitted against National Front leader Ms Le Pen in a May 7 head-to-head.

A defiant Mr Valls, 54, told his supporters the Socialist primary runoff next Sunday would be "a clear choice between unachievable promises and a credible left". Spanish-born Mr Valls set out to modernise his party but struggled to unite his camp, with his rivals accusing him of betraying leftist ideals by forcing through labour market reforms.

Mr Hamon, a traditional left winger sacked from government by Mr Hollande for criticising his economic policies, said he offered hope to a party ailing after five years under Mr Hollande, beset by economic sluggishness and mass protests.

Mr Hamon has attracted attention with a proposal to give the unemployed and the lowly-paid a "universal income" rising from €600 (S$915) to €750 a month.

Mr Valls has poured scorn on the idea.

Some Socialist heavyweights have hinted they could abandon their party's nominee and back Mr Macron instead if he looks to have a better chance of reaching the second round of the presidential election against Ms Le Pen.

Mr Macron himself has ruled out a pact with the Socialists, promising that his En Marche (On the Move) party will field hundreds of candidates in parliamentary elections in June.

Communist-backed firebrand Jean-Luc Melenchon, who like Mr Macron is standing as an independent, also threatens to split the left-wing vote.

The influence of Ms Le Pen, who leads the anti-immigration National Front, has overshadowed the entire presidential campaign so far.

She told a meeting of right-wing populist parties in Germany on Saturday that Europe was about to "wake up" following the victory of Mr Donald Trump in the US election and the British vote to leave the European Union.

AGENCE FRANCE- PRESSE, BLOOMBERG, REUTERS